Any node can become zoomable: add dimension via right-click

Visual distinction:
- Populated dimension: dashed cyan ring + [+] indicator
- Empty dimension: subtle gray dashed ring + [○] indicator
- No dimension: plain station (no ring)

Context menu changes:
- "Open dimension" on nodes that have children (zooms in directly)
- "Add dimension" on nodes without children (creates empty zoomable space)
- Removed old "Add child node" option

Add dimension creates an empty children structure on the node with
proper parent metadata. The node immediately shows the [○] indicator
and becomes zoomable. User enters and builds tracks with FAB + branch
handles. Truly recursive metro — any station can contain a world.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

resources/js/Components/MetroMap/MetroCanvas.vue

@@ -772,7 +772,7 @@ const renderDimension = (dimData, opacity, parentGroup) => {
         })
         .attr('stroke-width', 2)
 
-    // Child-dimension indicator
+    // Child-dimension indicator: populated dimension (has nodes inside)
     nodeGroups.filter(d => d.children && (d.children.nodes?.length ?? 0) > 0)
         .append('circle')
         .attr('r', 16)
@@ -783,7 +783,6 @@ const renderDimension = (dimData, opacity, parentGroup) => {
         .attr('opacity', 0.5)
         .attr('filter', 'url(#childGlow)')
 
-    // "[+]" label for nodes with children
     nodeGroups.filter(d => d.children && (d.children.nodes?.length ?? 0) > 0)
         .append('text')
         .attr('x', 13)
@@ -794,6 +793,26 @@ const renderDimension = (dimData, opacity, parentGroup) => {
         .attr('opacity', 0.8)
         .text('[+]')
 
+    // Empty dimension indicator (dimension exists but no nodes yet)
+    nodeGroups.filter(d => d.children && (d.children.nodes?.length ?? 0) === 0)
+        .append('circle')
+        .attr('r', 14)
+        .attr('fill', 'none')
+        .attr('stroke', '#8892b0')
+        .attr('stroke-width', 0.8)
+        .attr('stroke-dasharray', '2,4')
+        .attr('opacity', 0.4)
+
+    nodeGroups.filter(d => d.children && (d.children.nodes?.length ?? 0) === 0)
+        .append('text')
+        .attr('x', 13)
+        .attr('y', -13)
+        .attr('fill', '#8892b0')
+        .attr('font-family', "'VT323', monospace")
+        .attr('font-size', '10px')
+        .attr('opacity', 0.5)
+        .text('[○]')
+
     // Station label
     nodeGroups.append('text')
         .attr('x', 0)
@@ -880,22 +899,35 @@ const handleContextEdit = () => {
     closeContextMenu()
 }
 
-const handleContextAddChild = () => {
-    if (contextMenu.value.node) {
-        emit('create-node', {
-            x: contextMenu.value.canvasX,
-            y: contextMenu.value.canvasY,
-            parentNodeId: contextMenu.value.node.id,
-            parentEntityType: contextMenu.value.node.entityType ?? null,
-            parentEntityId: contextMenu.value.node.entityId ?? null,
-            dimensionId: contextMenu.value.node.id,
-            depth: currentDepth.value + 1,
-            addToNode: contextMenu.value.node,
-        })
+/** "Add dimension" — attach an empty children object to a node, making it zoomable */
+const handleContextAddDimension = () => {
+    const node = contextMenu.value.node
+    if (!node) { closeContextMenu(); return }
+
+    // Create empty dimension structure on the node
+    node.children = {
+        lines: [],
+        nodes: [],
+        connections: [],
+        parentEntityType: node.entityType ?? null,
+        parentEntityId: node.entityId ?? null,
+        parentName: node.name ?? null,
     }
+
+    // Re-render to show the new [○] indicator
+    renderMap()
     closeContextMenu()
 }
 
+/** "Open dimension" — zoom into a node that already has children */
+const handleContextZoomIn = () => {
+    const node = contextMenu.value.node
+    if (!node?.children) { closeContextMenu(); return }
+
+    closeContextMenu()
+    commitDimensionChange('in', node)
+}
+
 const handleContextDelete = () => {
     if (contextMenu.value.node) emit('delete-node', contextMenu.value.node)
     closeContextMenu()
@@ -1055,9 +1087,16 @@ defineExpose({
                     <button
                         v-if="contextMenu.node?.children"
                         class="context-item"
-                        @click="handleContextAddChild"
+                        @click="handleContextZoomIn"
                     >
-                        + Add child node
+                        &gt; Open dimension
+                    </button>
+                    <button
+                        v-if="!contextMenu.node?.children"
+                        class="context-item"
+                        @click="handleContextAddDimension"
+                    >
+                        + Add dimension
                     </button>
                     <button class="context-item danger" @click="handleContextDelete">Delete</button>
                 </template>